choosing the right electromotor, please help.

[MakkyBrown]

Hi Giel,

I dont have the specs on gand, but the more info tab under the picture of the motor on Banggood gives these specs.

Torque is also a function of motor speed, so you need one with good torque for cutting at low speeds.

Noise will also be a factor.  Motors for battery drills are quite noisy, too noisy for faceting.

The worm wheel drives the output shaft of the gearbox.  On my gearbox the shaft is 6mm od with a flat.  I drilled a 6mm hole in the end of a 10x10x60mm piece of mild steel, rotated 90 deg and drilled an offset hole for a tightening screw and split the end so it looks a bit like a battery terminal. 

Next time I wont do this, it requires too much pressure to clamp the arm to the shaft. Instead I'll just drill and tap a hole in the end, so I can screw a bolt straight down onto the flat on the shaft.

Then I split the rod so ut was 5mm wide except for the end with the hole, it stays as a 10x10x10mm bloc, and drilled and tapped 3 holes for 5mm bolts at, 15mm, 20mm and 25mm from the centre of the 6mm hole. These are mounting holes for the 5mm tie rod ends I use as a shaft.   They give a throw of 30  40, and 50mm respectively.

The tie rod ends are from Banggood, 1 male and 1 female + a tightening nut so I can adjust the length and position the end point of the oscillation.  They have a swivvel bearing at their end.

Makky,
I'm wondering if bush bearings would be better than ball bearings when accuracy is required,  a small amount of oil on the bearings would remove the play.

Motion Dynamice make

Given the quality and play in some of the ball bearings I have purchased from China maybe. Generally in these little motors I think the ball bearings give a longer service life. Some of the smaller dc motors we have purchased with brass bearings have a very short service life, like 150hours from their datasheets. The front ball bearing in your 775 is good imo.
I suppose the next step up would be a motor like the printer motor I have where there is preload between the front and rear bearings and a service life of thousands of hours.

[FlashGP]

Agree.  Preloading should also help with runout.

If I had a lathe, I would set up the motor separately from the oscillating shaft and run it via a belt.  This would allow the motor to be changed or upgraded easily.  A similar concept to the VJ but without the flex drive and using a separate oscillator driver so it cant be oscillated too fast.

Basically 2 linear bearungs holding a tube bearing which osillates using a yoke that pushes and pulls a flange or tab on the tube.  A keyed pulley mounted between guide bearings to keep it stationary with respect to the base and a shaft running through the pulley with flanges each side of the tube so the tube bearing   pushes and pulls the central shaft.

Regards
Gordon

[MakkyBrown]

In this clip you'll see the Polymetric Scintillator 88 mast/faceting head on the concave machine etc. (at roughly 28-33 seconds) What I would like to know is how have they setup the bearings for the horizontal pivot on the mast. Any ideas?? I want to use a pivot like that but it's hard to figure out which bearings especially the rubbish I recently got from china. I'm a bit lost for ideas that will be rock solid and precise. Maybe I'll have to use tapered roller/cone bearings.

https://www.youtube.com/watch?v=Q1oBOCm0V-o
https://www.polymetricinc.com/home_htm_files/76.jpg

CheersMB

[Rusted]

Why would you need to go with ball or roller bearings for that pivot? Brass or bronze or Delron would work  and could be machined to whatever tolerance you want.
Delron is beautiful stuff to work with.

[MakkyBrown]

Delron is nice I've used it a bit. It has to take all the side to side movement of the hand piece and I was thinking bearings would be smoother.

[MakkyBrown]

Delron is nice I've used it a bit. It has to take all the side to side movement of the hand piece and I was thinking bearings would be smoother.

Solved, i'm going to recess a couple of thrust bearings.

[Giel]

Milestone in the project! I have made up my mind about  the motor! 
This is the lucky one:
https://www.omc-stepperonline.com/brushless-dc-motor/24v-3500rpm-023nm-84w-50a-%D1%8457x49mm-brushless-dc-motor-57blr50-24-01.html

Its small, I think the torque is enough, if not I can always buy a stronger one from the same series.

Other components are also slowly coming in; brackets and linear shafts, linear scales (or whatever the name is) etc etc. Cleaned and mounted the bearings, running smooth and no play.

[MakkyBrown]

  what motor driver did you get? Did you go with theirs or a cheap one off ebay? You should be happy with that motor if it's the same quality as their steppers. And a massive 8mm shaft
Looking very flash with the digital readouts.

[Giel]

I didnt order yet, but I will buy their driver with it. Big thanx for that link Makky!

Looking very flash with the digital readouts.

Hahaha, I thought they were pretty cheap, and after all I need to know where the spindle is, I liked that the readout is separate so I can build it in.

I am thinking about how to make the spindle head itself now;
I have one of these:https://www.ebay.nl/itm/50Collet-Chuck-Holder-CNC-Milling-Extension-Rod-Straight-Shank-C10-ER16A-150L/142057947085?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
And want to combine it with these:https://www.damencnc.com/nl/fk10-fixed-ballscrew-support-units-c3-quality/a1431
and one of these: https://www.damencnc.com/nl/60x60-servo-motor-bracket-mba10-d/a2109?c=314
and the motor inline with a shaft coupler. (thought this was more easy than explaining without the links.

Do you think one of those bearings is enough, or do I need two?
Anyways thanx for all the input!

[MakkyBrown]

Yeah, nice idea. I'll been doing a similar thing to this on my new faceting machine to drive my index/quill. But on a smaller scale and making it myself.  They are pretty expensive brackets though but look pretty accurate.
Have you seen these
https://www.aliexpress.com/item/57-stepper-motor-bracket-nema-23-fixed-seat-connecting-seat-support-seat/32821387669.html?spm=2114.10010108.1000014.1.152543128OUBnL&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.13338.106568.000000000000000&scm_id=1007.13338.106568.000000000000000&scm-url=1007.13338.106568.000000000000000&pvid=18b8900f-acb4-4050-8e56-f30689f2cd71
https://www.aliexpress.com/item/CNC-NEMA-23-Stepper-Motor-Accessories-Mounts-Bracket-Support-Shelf-nema23-Stepping-Motor-For-57-Motor/32960143402.html?spm=2114.search0104.3.106.172b4bebxCxMT2&ws_ab_test=searchweb0_0,searchweb201602_10_10065_10068_10130_10547_319_317_10548_10696_453_10084_454_10083_10618_10307_537_536_10131_10132_10902_10133_10059_10884_10887_321_322_10103,searchweb201603_55,ppcSwitch_0&algo_expid=e278efb4-2513-43ec-b0ab-08a9845ff413-16&algo_pvid=e278efb4-2513-43ec-b0ab-08a9845ff413&transAbTest=ae803_4
Maybe you could make your own bearing holder with adjusters to line up perfectly.

I think one bearing but good quality.
But you could still go the simplest option and just adapt straight to the motor shaft. It is 8mm and there are a good few replacement motors in the cost of the bracket/bearing.https://www.aliexpress.com/item/ER11-ER16-ER20-C16-C20-C25-Motor-Shaft-Extension-Rod-Spindle-Collet-Lathe-Tools-Holder-Inner/32968409344.html?spm=2114.search0104.3.1.68cf6b7d2uLnSe&ws_ab_test=searchweb0_0,searchweb201602_10_10065_10068_10130_10547_319_317_10548_10696_453_10084_454_10083_10618_10307_537_536_10131_10132_10902_10133_10059_10884_10887_321_322_10103,searchweb201603_55,ppcSwitch_0&algo_expid=3745efe0-ef3f-4ed1-ac3f-c836df7e5e3d-0&algo_pvid=3745efe0-ef3f-4ed1-ac3f-c836df7e5e3d&transAbTest=ae803_4

[MakkyBrown]

Just been thinking, oscilation might be nicer on a feed screw.  Using endstops for safely and homing and an arduino+motor driver to reverse direction and control the speed and thus do nice slow down transition as it changes direction. And I just happen to have another motor from the printer with an encoder on it.

And I just purchase one other those collet holders for my little printer motor.  , no I'm not going to build one.    maybe.........

[Giel]

I just ordered the motor.
I will also have a look at those brackets, maybe it's a good option, I thought about making the bracket, or better maybe; let someone make it, since I dont have a cnc machine. A bracket with 2 good bearings! (better safe than sorry!)
There is a big community of "makers" in my town with 3d printers, cnc machines etc. so I will find someone that can make it.
The machine project is slow now, as I am busy with work, the garden and other things, but I will post it on the forum if I make some progress.

I did however buy a very small lathe this week on a dutch second hand site, I have always wanted a small lathe so I just could not help myself.
Seller said it needs some love, paid 100 euro for it. I think it is a small jewellers lathe or a watchmakers lathe, it has about 20 cm between centers.

[FlashGP]

Hi Giel,


I'm envious of the mini lathe, although I don't know how precise it is.  I recommend getting a dial indicator on an arm with magnet base so you can check your work, etc. 


There are some great YouTube videos by Joe Pieczynski that talk about machining in terms dummies like me can understand.  In one, he shows you how to accurately center your job even if the chuck is off center.  He made something like a collett for the chuck.


Makky, I had discounted the extension tools for the ER11 etc as creating too much length.  BUT I hadn't thought of mounting the shaft in a sintered bronze bearing with oil hole and driving the shaft.  This would certainly get rid of the runout resulting from mounting a collet holder on the motor shaft.  But it would require a close fit with the bearings. 


Mounting the motor behind the shaft with a flexible coupling would add length, it may be better to drive the shaft with a belt like the Polymetric concave facetor does.


regards
Gordon

[MakkyBrown]

Flash, I'll let you know how much run out I get from my cheap $7 ER11 adapter when it arrives.

Giel, Nice little lathe, bit of a bargain for the $$.

[MakkyBrown]

Flash or anyone, how many mm of oscillation do I need ?